1. Field of the Invention
The present invention relates to armaments and more particularly to guided munitions. Even more particularly, the invention relates to a method and system for guiding and controlling a munition by making corrections to the trajectory based on bore sight angle verses time history.
2. Background Information
Mortars are one of the most commonly employed weapons in a ground combat unit. The traditional role of mortars has been to provide close and continuous fire support for maneuvering forces. Military history has repeatedly demonstrated the effectiveness of mortars. Their rapid, high-angle, plunging fires are invaluable against dug-in enemy troops and targets in defilade, which are not vulnerable to attack by direct fires. One of the major disadvantages of mortars is their comparatively low accuracy, and as a result mortars are becoming less effective in today's precision combat environment. Equipping a mortar round with a precision guidance package will increase its accuracy, enabling the mortar to be a precision munition that will be significantly more effective in wartime situations. For maximum utility, the guidance package preferably should be an inexpensive retrofit to current munitions, with a cost in production that allows its use in all situations, either as a guided or unguided weapon.
Unguided munitions are subject to aim error and wind disturbances. These often cause the munition to miss the target completely or require many rounds to complete the fire mission due to the large CEP (Circular Error Probability). Current approaches to guided weapons are expensive and are used on larger long range weapons. The approach described in this disclosure results in significantly lower cost and smaller size. This allows use with small to medium caliber weapons and significantly improves CEP which also results in a significant reduction in the quantity of rounds required to complete the fire mission which in turn results in lower overall cost and improved crew survivability. In addition, another benefit to this approach is the virtual elimination of collateral damage due to errant rounds impacting non-targeted areas.
Mortars are typically unguided or guided by an expensive G&C (guidance and control) system. The cost is high for current guided mortars and unguided mortars have poor accuracy. Also, unguided mortars result in unacceptable collateral damage, excess cost due to large number of rounds required to blanket target area, and expose the mortar crew to counterbattery fire due to large time required to drop the necessary shells to saturate the target.
Unlike powered rockets, mortars and ballistic rounds travel in a ballistic path. It is possible to modify the round by adding large control surfaces so that it can glide. However, this modification requires large wings which could destabilize smaller caliber rounds. In addition, large wings must retract to allow launch from a gun. The large retractable wings are mechanically complex and expensive. A low cost alternative is based on nose mounted canards. In this case, the projectiles maneuverability is limited to less than one G. Thus, the round must take a ballistic path to the target. It is not possible to use a direct homing approach because the target's desired look angle is not at bore sight for a ballistic path and the control surfaces do not have sufficient maneuver capacity to cause the round to fly straight to the target. Platforms such as rockets are able to approach a target in a direct (non-ballistic) path. However this approach is not practical for an unpowered mortar or munition which normally follows only a ballistic trajectory.
The prior art apparatus, systems and methods require considerable, complex, hardware into which a guidance algorithm is integrated. This drives the cost of the individual round excessively and impacts overall round performance, requiring special compensation, for example, to preserve stability. Prior art apparatus suffer from a large CEP and possess no capability against moving targets, this being directly attributable to the highly limited maneuver basket. Prior methods also required costly hardware to support the guidance algorithm integration.
For the basic mortar/small caliber munition there is currently no satisfactory method of guidance and control. For large caliber weapons, a terminal seeker with a direct approach to the target can be incorporated. Use of a direct approach limits the maneuver range. All known existing methods are of little practical use due to cost and accuracy limitations for small and medium caliber munitions.
Therefore there is a need for an accurate and cost effective means for guiding small caliber munitions which follow a ballistic path toward a target, such as mortar shells. There is also a need for an ultra low cost G&C approach for mortar shells which is compatible with a large class of rounds. Also a control algorithm and method is needed to steer a mortar or munition having a limited maneuverability when coupled with appropriate aerodynamic controls. Furthermore, there is a need for a control algorithm that significantly improves mortar/munition terminal accuracy, resulting in reduced cost to prosecute the target, minimizes collateral damage, and increases crew survivability.